Figure 1: Macroscopic observation and histology of the tibial cartilage of a 3-month-old (a, c) and 12-month-old (b, d) Dunkin Hartley guinea pigs. No cartilage degeneration is observable at 3 months. In contrast, at 12 months, the cartilage is degenerated with erosion and fragmentation on the medial side. Reprinted with permission from [25].